The adrenal or suprarenal glands are two important stress response pathways. The adrenal glands are located on top of the kidneys and secrete a few different types of hormones related to controlling the body’s metabolism, the body’s response to perceived stress, regulation of blood pressure, and development of secondary sexual characteristics.

Let’s focus on the role of the adrenals in the stress response. Before discussing the adrenal glands’ role, we need to zoom out and look at the bigger picture, as we have different pathways and physiological responses to a perceived stressor. The sympathetic nervous system responds directly to a perceived stressor by stimulating peripheral organs by means of the sympathetic nervous system, it also promotes the release of adrenaline and noradrenaline (the so-called cathecholamines) into the bloodstream. In the latter case the adrenals play a role: in response to a stressor – whatever it may be – your adrenal glands are triggered to release adrenaline and noradrenaline.

To fight or to flight?

Adrenaline and noradrenaline are the two hormones responsible for the initial physical changes when we are in our sympathetic state: the heart rate goes up, respiration rate goes up, pupils widen, blood is being redirected away from the digestive and reproductive organs, and so on. All these changes are needed to respond to the source of stress. Our two options are: flight or fight. Scientists refer to this pathway (stressor – sympathetic activation – stimulation of the adrenal glands – release of adrenaline and noradrenaline) as the Sympathetic-Arenomedullary System (SAM). At the same time, the sympathetic nervous system promotes the liver to produce glucose (gluconeogenesis), and the fat tissue to release free fatty acids (lipolysis). These can all be used as fuel for the expected physical activity involved in fighting or fleeing.

The Hypothamus-Pituitary- Adrenal axis (HPA)

However, there is another complex pathway of events in the body, which is being activated in response to stress: this is the hypothalamus-pituitary- adrenal axis (HPA). It is thought to provide a relatively slower, but amplified and sustained stress response. Due to its location in the midbrain, the hypothalamus is sensitive to an emotion in response to the stressor. The stressor thus triggers production and the release of adrenaline and nor-adrenaline via the SAM pathway from the adrenal glands but simultaneously the other pathway, the HPA axis is being activated, and the following occurs:

Corticotropin-releasing hormone (CRH), and anti-diuretic hormone (ADH) are being released in the hypothalamus

CRH stimulates the secretion of adrenocorticotropic hormone (ACTH) from the pituitary

The released ADH by the hypothalamus directly triggers reabsorption of water by the kidneys and induces narrowing of the blood vessels (vasoconstriction), thus raising blood pressure.

Cortisol itself feeds back to the brain to shut off further cortisol secretion.

This negative feedback loop protects the organism from prolonged, detrimental cortisol exposure and keeps its concentration within a wide but stable operating range. However, under sustained perceived stress this feedback mechanism is impaired.

Cortisol, SAM and HPA

Cortisol and other glucocorticoids bring about a variety of physiological changes to deal with a threat or stressor: it stimulates lipolysis, increases gluconeogenesis in the liver, decreases insulin production in the pancreas, and increases insulin resistance. Notice how decreased insulin production and increased insulin resistance raises levels of plasma glucose.

Thus, together with rapid SAM action, the somewhat slower and longer- lasting action of the HPA axis ensures a proper response to threat and aims to restore homeostasis across multiple organ systems. 115 Under long-term perceived stress, the production of adrenaline and noradrenaline (through the SAM pathway) halts, while cortisol via the HPA axis remains to be secreted.

One important difference between SAM and the HPA axis is the way they affect the immune system. The SAM system activates the inflammatory response, whereas cortisol (from the HPA pathway) has been shown to decrease the number of circulating cells from the immune system (leukocytes) and inhibit the migration of those cells to the site of injury or infection.

As previously explained, we actually benefit from the short-term effects of cortisol through gluconeogenesis (formation of glucose from protein and fat sources) and the anti-stress and anti-inflammatory response (suppression of the immune system), In the long term, these exact same effects are detrimental to our health. Suppression of our immune systems makes us prone to diseases. High levels of cortisol have also been linked to the development of osteoporosis and issues with joints because cortisol reduces bone formation, hinders calcium uptake in the intestines and inhibits the production of collagen (an important component of joints and connective tissue in general.

Yoga Therapy: work on both relaxation and awareness development

Why should you, as a yoga teacher or therapist, know about this? First of all, stress is a large contributor to many diseases. Whatever somebody comes to you about, I feel that invoking relaxation is one of the most effective first steps to take in a therapeutic setting. Remember that relaxation and restorative practices are very powerful in breaking the cycle of long-term stress. I like to start my sessions with a long body scan or yoga nidra, and often clients respond that they haven’t felt so relaxed in a long time.

Scientists have found another distinction between SAM and HPA axis activation, although I would like to point out that that there remains some debate on this point. Apparently, we have the ability to make a distinction between stressors and activate either pathway accordingly. Uncontrollable stressors and stressors that are marked as threats are related to a high HPA axis activation. When the stress, or threat, especially violates our confidence (think of public embarrassment or failure) we have especially high levels of cortisol. Controllable stressors – stressors that are viewed as a challenge – are related to a high SAM activation. Yoga practices, especially meditation, can greatly help us to define the stressor, rather then let our impulses take control.

If you do something ‘wrong’ you can take it as a failure, or you can take it as a motivation to improve yourself and do better. Think of Charlie Parker, the famous jazz musician who got a cymbal thrown at him by another musician when he blew up on stage: he was publicly embarrassed. However, he knew he had talent and something new to bring to the jazz music scene, so he persisted, only to come back a year later and prove his status as a revolutionary musician. By developing the ability to look objectively at a situation or stressor, we can manage to see a situation as challenging rather than life threatening and ego-shattering.

The physiological effects of relaxation through meditation have been described by many authors. One of them is Herbert Benson, an American medical doctor, cardiologist, and one of the first to study the effects of meditation (Transcendental Meditation, TM, in this case) on human physiology. The relaxation response is the exact opposite of the stress response (funnily enough both responses were studied in the exact same room at the Harvard Medical School). According to Benson, two important facets in evoking the relaxation response are having a ‘mental device’ to which we can bring our attention (e.g., mantra or breath) to keep the mind from wandering and, secondly, a passive attitude.118 I tend to believe that a combination of this type of one-pointed focus meditation (to invoke the relaxation response) and changing our perception of every day life and its stressors (so that we do not illicit the stress response in the first place) is the key to ultimate health and happiness. For this reason, as yoga therapists, we work on both relaxation and awareness development.